/*
 * 11/19/04		1.0 moved to LGPL.
 * 12/12/99		Initial version.	mdm@techie.com
 *-----------------------------------------------------------------------
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library General Public License as published
 *   by the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this program; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *----------------------------------------------------------------------
 */

package javazoom.jl.decoder;

/**
 * The <code>Equalizer</code> class can be used to specify equalization settings
 * for the MPEG audio decoder.
 * <p>
 * The equalizer consists of 32 band-pass filters. Each band of the equalizer
 * can take on a fractional value between -1.0 and +1.0. At -1.0, the input
 * signal is attenuated by 6dB, at +1.0 the signal is amplified by 6dB.
 * 
 * @see Decoder
 * 
 * @author MDM
 */
public final class Equalizer {
	/**
	 * Equalizer setting to denote that a given band will not be present in the
	 * output signal.
	 */
	public static final float BAND_NOT_PRESENT = Float.NEGATIVE_INFINITY;

	public static final Equalizer PASS_THRU_EQ = new Equalizer();

	private static final int BANDS = 32;

	private final float[] settings = new float[BANDS];

	/**
	 * Creates a new <code>Equalizer</code> instance.
	 */
	public Equalizer() {
	}

//	private Equalizer(float b1, float b2, float b3, float b4, float b5,
//					 float b6, float b7, float b8, float b9, float b10, float b11,
//					 float b12, float b13, float b14, float b15, float b16,
//					 float b17, float b18, float b19, float b20);

	public Equalizer(float[] settings) {
		setFrom(settings);
	}

	public Equalizer(EQFunction eq) {
		setFrom(eq);
	}

	public void setFrom(float[] eq) {
		reset();
		int max = (eq.length > BANDS) ? BANDS : eq.length;

		for (int i = 0; i < max; i++) {
			settings[i] = limit(eq[i]);
		}
	}

	public void setFrom(EQFunction eq) {
		reset();
		int max = BANDS;

		for (int i = 0; i < max; i++) {
			settings[i] = limit(eq.getBand(i));
		}
	}

	/**
	 * Sets the bands of this equalizer to the value the bands of another equalizer.
	 * Bands that are not present in both equalizers are ignored.
	 */
	public void setFrom(Equalizer eq) {
		if (eq != this) {
			setFrom(eq.settings);
		}
	}

	/**
	 * Sets all bands to 0.0
	 */
	public void reset() {
		for (int i = 0; i < BANDS; i++) {
			settings[i] = 0.0f;
		}
	}

	/**
	 * Retrieves the number of bands present in this equalizer.
	 */
	public int getBandCount() {
		return settings.length;
	}

	public float setBand(int band, float neweq) {
		float eq = 0.0f;

		if ((band >= 0) && (band < BANDS)) {
			eq = settings[band];
			settings[band] = limit(neweq);
		}

		return eq;
	}

	/**
	 * Retrieves the EQ setting for a given band.
	 */
	public float getBand(int band) {
		float eq = 0.0f;

		if ((band >= 0) && (band < BANDS)) {
			eq = settings[band];
		}

		return eq;
	}

	private float limit(float eq) {
		if (eq == BAND_NOT_PRESENT)
			return eq;
		if (eq > 1.0f)
			return 1.0f;
		if (eq < -1.0f)
			return -1.0f;

		return eq;
	}

	/**
	 * Retrieves an array of floats whose values represent a scaling factor that can
	 * be applied to linear samples in each band to provide the equalization
	 * represented by this instance.
	 * 
	 * @return an array of factors that can be applied to the subbands.
	 */
	float[] getBandFactors() {
		float[] factors = new float[BANDS];
		for (int i = 0, maxCount = BANDS; i < maxCount; i++) {
			factors[i] = getBandFactor(settings[i]);
		}

		return factors;
	}

	/**
	 * Converts an equalizer band setting to a sample factor. The factor is
	 * determined by the function f = 2^n where n is the equalizer band setting in
	 * the range [-1.0,1.0].
	 * 
	 */
	float getBandFactor(float eq) {
		if (eq == BAND_NOT_PRESENT)
			return 0.0f;

		float f = (float) Math.pow(2.0, eq);
		return f;
	}

	public abstract static class EQFunction {
		/**
		 * Returns the setting of a band in the equalizer.
		 * 
		 * @param band The index of the band to retrieve the setting for.
		 * 
		 * @return the setting of the specified band. This is a value between -1 and +1.
		 */
		public float getBand(int band) {
			return 0.0f;
		}

	}

}
